Method and apparatus for transmitting and receiving channel state information in wireless communication system

ABSTRACT

A method and an apparatus are provided for transmitting channel state information of a terminal is provided. A first Channel State Information Reference Signal (CSI-RS) and a second CSI-RS are received. Channel State Information (CSI) is generated based on both the first CSI-RS and the second CSI-RS. The CSI is transmitted.

PRIORITY

This application claims priority under 35 U.S.C. 119(a) to applicationsfiled in the Korean Intellectual Property Office on Sep. 18, 2012 andOct. 12, 2012, and assigned Serial Nos. 10-2012-0103431 and10-2012-0113608, respectively, the contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a channel state informationtransmission/reception method and apparatus and, more particularly, to amethod and apparatus for transmitting and receiving channel stateinformation in a wireless communication system supporting a plurality ofantennas.

2. Description of the Related Art

A Reference Signal (RS) is used to measure the channel state (orquality) between a base station and users (such as, for example, signalstrength and distortion, interference strength, and Gaussian noise), andis used in demodulation and decoding of a received data symbol in awireless mobile communication system. The reference signal is also tomeasure a radio channel state. The receiver measures the strength of thereference signal transmitted by the transmitter at a predeterminedtransmit power to determine the radio channel state between the receiverand the transmitter. The receiver sends a request to the transmitter fora data rate based on the determined radio channel state.

The 3^(rd) generation evolved mobile communication standards such as,for example, the 3^(rd) Generation Partnership Project Long TermEvolution-Advanced (3GPP LTE-A) and Institute of Electrical andElectronics Engineers (IEEE) 802.16m, adopt a multi-carrier multipleaccess technique such as Orthogonal Frequency Division Multiplexing(Multiple Access) (OFDM(A)). In the case of a multi-carrier multipleaccess-based wireless mobile communication system, the channelestimation and measurement performance is influenced by the number ofsymbols and the number of subcarriers to which the reference signal ismapped on the time-frequency resource grid. The channel estimation andmeasurement performance is also influenced by the power allocated forreference signal transmission. Accordingly, by allocating more radioresources (including time, frequency, and power), it is possible toimprove channel estimation and measurement performance, resulting inimproved received data symbol demodulation and decoding performance andchannel state measurement accuracy.

In a resource-constrained mobile communication system, however, if theradio resource is allocated for transmitting resource signals, theresource amount for data signal transmission is reduced. For thisreason, the resource amount for the reference signal transmission isdetermined by taking the system throughput into account. Particularly,in a Multiple Input Multiple Output (MIMO) system including a pluralityof antennas, a key issue is how to design and measure reference signals.

SUMMARY OF THE INVENTION

The present invention has been made to address at least the aboveproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of the present inventionprovides a method and apparatus for efficiently transmitting/receivingchannel state information.

Another aspect of the present invention provides a method and apparatusfor efficiently transmitting/receiving the channel state informationwhen using a plurality of antennas.

In accordance with an aspect of the present invention, a method fortransmitting channel state information of a terminal is provided. Afirst Channel State Information Reference Signal (CSI-RS) and a secondCSI-RS are received. Channel State Information (CSI) is generated basedon both the first CSI-RS and the second CSI-RS. The CSI is transmitted.

In accordance with another aspect of the present disclosure, a terminalfor transmitting channel state information is provided. The terminalincludes a receiver that receives a first CSI-RS and a second CSI-RS.The terminal also includes a controller that generates CSI based on boththe first CSI-RS and the second CSI-RS. The terminal further includes atransmitter that transmits the CSI.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptionwhen taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a Full Dimension MIMO (FD-MIMO) system;

FIG. 2 is a time-frequency grid illustrating a single Resource Block(RB) of a downlink subframe as a smallest scheduling unit in theLTE/LTE-A system;

FIG. 3 is a diagram illustrating a mechanism for CSI-RS transmission inFD-MIMO system, according to an embodiment of the present invention;

FIG. 4 is a diagram illustrating a mechanism for transmitting RankIndicator (RI), Precoding Matrix Indicator (PMI), and Channel QualityIndicator (CQI) based on two CSI-RS in the feedback method, according toan embodiment of the present invention;

FIG. 5 is a diagram illustrating a mechanism for transmitting channelstate information, according to an embodiment of the present invention;

FIG. 6 is a diagram illustrating a mechanism for transmitting channelstate information, according to an embodiment of the present invention;

FIG. 7 is a diagram illustrating a mechanism for transmitting channelstate information, according to another embodiment of the presentinvention;

FIG. 8 is a diagram illustrating a mechanism for transmitting channelstate information, according to another embodiment of the presentinvention;

FIG. 9 is a diagram illustrating a mechanism for transmitting channelstate information, according to another embodiment of the presentinvention;

FIG. 10 is a diagram illustrating a mechanism for transmitting channelstate information, according to another embodiment of the presentinvention;

FIG. 11 is a flowchart illustrating an eNB procedure of configuringchannel state information feedback of the User Equipment (UE) in aFD-MIMO system, according to an embodiment of the present invention;

FIG. 12 is a flowchart illustrating a UE procedure for transmitting thechannel state information based on the configuration indicated by theevolved Node B (eNB) in the FD-MIMO system, according to an embodimentof the present invention;

FIG. 13 is a block diagram illustrating a configuration of the eNB,according to an embodiment of the present invention; and

FIG. 14 is a block diagram illustrating a configuration the UE,according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

Embodiments of the present invention are described in detail withreference to the accompanying drawings. The same or similar componentsmay be designated by the same or similar reference numerals althoughthey are illustrated in different drawings. Detailed descriptions ofconstructions or processes known in the art may be omitted to avoidobscuring the subject matter of the present disclosure.

The following terms are defined in consideration of the functionality inembodiments of the present invention, and may vary according to theintention of a user or an operator, usage, etc. Therefore, thedefinition should be made on the basis of the overall content of thepresent specification.

Although the description is directed to an OFDM-based radiocommunication system, particularly, the 3GPP Evolved UniversalTerrestrial Radio Access (E-UTRA), it will be understood by thoseskilled in the art that embodiments of the present invention can beapplied to other communication systems having a similar technicalbackground and channel format, with a slight modification, withoutdeparting from the spirit and scope of the present invention.

Embodiments of the present invention relate to a wireless mobilecommunication system and, in particular, to a method for efficientlytransmitting/receiving channel state information in a wireless mobilecommunication system operating with a multicarrier multiple accessscheme such as, for example, Orthogonal Frequency Division MultipleAccess (OFDMA).

Mobile communication systems have evolved into high-speed, high-qualitywireless packet data communication systems that provide data andmultimedia services beyond the early voice-oriented services. Recently,various mobile communication standards, such as, for example, High SpeedDownlink Packet Access (HSDPA), High Speed Uplink Packet Access (HSUPA),LTE, and LTE-A defined in 3^(rd) Generation Partnership Project (3GPP),High Rate Packet Data (HRPD) defined in 3^(rd) Generation PartnershipProject-2 (3GPP2), and 802.16 defined in IEEE, have been developed tosupport the high-speed, high-quality wireless packet data communicationservices.

Existing 3^(rd) generation mobile communications, including LTE, UltraMobile Broadband (UMB), and 802.16m, operate based on a multi-carriermultiple access scheme and adopt Multiple Input Multiple Output (MIMO)with channel sensitive scheduling, such as beamforming and AdaptiveModulation and Coding (AMC), to improve transmission efficiency. Thesetechniques increase the system throughput by improving transmissionefficiency in such a way as to concentrate transmit power of a pluralityof antennas, adjusting an amount of transmit data, and selectivelytransmitting data to the user with a best channel quality. Since most ofthese techniques operate based on the channel state information betweenthe base station (eNB) and the terminal (UE or Mobile Station (MS)), theeNB or UE has to measure the channel state between the eNB and the UE.At this time, the signal used for channel state measurement is a ChannelState Indication Reference Signal (CSI-RS). The eNB is a transmitter indownlink and a receiver in uplink. The one eNB may manage a plurality ofcells for transmission/reception. A mobile communication system includesa plurality of eNBs distributed geographically, and each eNB performstransmission/reception through a plurality of cells.

Existing 3^(rd) and 4^(th) Generation mobile communication systemsrepresented by LTE/LTE-A adopt a MIMO scheme with a plurality oftransmit and receive antennas to transmit a plurality of informationstreams as spatially separated. This technique of transmitting theplurality of information streams as spatially separated is referred toas spatial multiplexing. Typically, the number of information streamscapable of being spatially multiplexed depends on the number of antennasof the transmitter and the receiver. The number of information streamsthat can be spatially multiplexed is referred to rank in general. In thecase of the MIMO scheme till the standard of LTE/LTE-A Release 11, thespatial multiplexing of up to 8×8 antennas and up to rank 8 aresupported.

The FD-MIMO system, to which a technique proposed in an embodiment ofthe present invention is applied, has been evolved from the LTE/LTE-AMIMO system supporting up to 8 transmit antennas so as to support 32 ormore transmit antennas. However, the scope of the present invention isnot limited thereto.

FIG. 1 is a diagram illustrating an FD-MIMO system. The FD-MIMO systemis a wireless communication system that is capable of transmitting datausing a few dozen or more transmit antennas.

Referring to FIG. 1, a base station transmitter 100 transmits radiosignals 120 and 130 through a few dozen or more transmit antennas.Transmit antennas 110 are arranged at a minimum distance among eachother. The minimum distance may be half of the wavelength (λ/2) of theradio signal. Typically, when the transmit antennas are arranged at thedistance of half of the wavelength of the radio signal, the signalstransmitted by the respective transmit antennas are influenced by theradio channel with low correlation. Assuming a radio signal band of 2GHz, this distance is 7.5 cm, and is shortened as the band becomeshigher than 2 GHz.

In FIG. 1, a few dozen or more transmit antennas 110 arranged at thebase station are used to transmit signals to one or more terminals asdenoted by reference numerals 120 and 130. In order to transmit signalsto a plurality of terminals simultaneously, an appropriated precoding isapplied. One terminal may receive a plurality of information streams.Typically, a number of information streams that a terminal can receiveis determined depending on the number of receive antennas of theterminal, channel state, and reception capability of the terminal.

In order to efficiently implement the FD-MIMO system, the terminal hasto accurately measure the channel condition and interference size andefficiently transmit the channel state information to the base station.If the channel state information is received, the base stationdetermines the terminals for downlink transmission, downlink data rate,and precoding to be applied. In the case of an FD-MIMO system using alarge number of transmit antennas, if the channel state informationtransmission method of the legacy LTE/LTE-A system is applied withoutmodification, the amount of control information to be transmitted inuplink significantly increases, resulting in uplink overhead.

The mobile communication system is restricted in resources such as, forexample, time, frequency, and transmission power. Accordingly, if aresource allocated for a reference signal increases, the resource amountto be allocated for data traffic channel transmission decreases,resulting in a reduction in the amount of data transmission. Althoughthe channel estimation and measurement performance are improved, thedata transmission amount decreases, resulting in reduction of entiresystem throughput. Thus, there is a need for efficiently allocatingresources for reference signal and traffic channel transmissions inorder to maximize the entire system throughput.

FIG. 2 is a time-frequency grid illustrating a single RB of a downlinksubframe as a smallest scheduling unit in the LTE/LTE-A system.

As shown in FIG. 2, the radio resource is of one subframe in the timedomain and one RB in the frequency domain. The radio resource consistsof 12 subcarriers in the frequency domain and 14 OFDM symbols in thetime domain, i.e., 168 unique frequency-time positions. In LTE/LTE-A,each frequency-time position is referred to as a Resource Element (RE).

The radio resource structured as shown in FIG. 2 can be used fortransmitting different types of signals as follows.

1. Cell-specific Reference Signal (CRS): reference signal transmitted toall the UEs within a cell

2. Demodulation Reference Signal (DMRS): reference signal transmitted toa specific UE

3. Physical Downlink Shared Channel (PDSCH): data channel transmitted indownlink, which the eNB uses to transmit data to the UE, and mapped toREs not used for reference signal transmission in a data region of FIG.2

4. Channel State Information Reference Signal (CSI-RS): reference signaltransmitted to the UEs within a cell and used for channel statemeasurement. Multiple CSI-RSs can be transmitted within a cell

5. Physical Hybrid-ARQ Indicator Channel (PHICH), Physical ControlFormat Indicator Channel (PCFICH), Physical Downlink Control Channel(PDCCH): channels for providing a control channel necessary for the UEto receive PDCCH and transmitting ACK/NACK of HARQ operation for uplinkdata transmission

In addition to the above signals, zero power CSI-RS can be configured inorder for the UEs within the corresponding cells to receive the CSI-RSstransmitted by different eNBs in the LTE-A system. The zero power CSI-RS(muting) can be mapped to the positions designated for CSI-RS, and theUE receives the traffic signal skipping the corresponding radio resourcein general. In the LTE-A system, the zero power CSI-RS is referred to asmuting. The zero power CSI-RS (muting) by nature is mapped to the CSI-RSposition without transmission power allocation.

In FIG. 2, the CSI-RS can be transmitted at some of the positions markedby A, B, C, D, E, F, G, H, I, and J, according to the number of numberof antennas transmitting CSI-RS. Also, the zero power CSI-RS (muting)can be mapped to some of the positions A, B, C, D, E, F, G, H, I, and J.The CSI-RS can be mapped to 2, 4, or 8 REs, according to the number ofantenna ports for transmission. For two antenna ports, half of aspecific pattern is used for CSI-RS transmission. For four antennaports, an entire specific pattern is used for CSI-RS transmission. Foreight antenna ports, two patterns are used for CSI-RS transmission.Muting is always performed by pattern. Specifically, although muting maybe applied to a plurality of patterns, if the muting positions mismatchCSI-RS positions, it cannot be partially applied to one pattern.

When transmitting CSI-RSs of two antenna ports, the CSI-RSs are mappedto two consecutive REs in the time domain and distinguished from eachother using orthogonal codes. When transmitting CSI-RSs of four antennaports, the CSI-RSs are mapped in the same way of mapping the two moreCSI-RSs to two more consecutive REs. This is applied to the case oftransmitting CSI-RSs of eight antenna ports.

In a cellular system, the reference signal has to be transmitted fordownlink channel state measurement. In the case of the 3GPP LTE-Asystem, the UE measures the channel state with the eNB using the CSI-RStransmitted by the eNB. The channel state is measured in considerationof a few factors including downlink interference. The downlinkinterference includes the interference caused by the antennas ofneighbor eNBs and thermal noise that are important in determining thedownlink channel condition. For example, when an eNB with one transmitantenna transmits a reference signal to a UE with one receive antenna,the UE has to determine an energy per symbol that can be received indownlink and an interference amount that may be received for theduration of receiving the corresponding symbol to calculate Es/Io fromthe received reference signal. The calculated Es/Io is reported to theeNB such that the eNB determines the downlink data rate for the UE.

In the LTE-A system, the UE feeds back the information on the downlinkchannel state for use in downlink scheduling of the eNB. Specifically,the UE measures the reference signal transmitted by the eNB in downlinkand feeds back the information estimated from the reference signal tothe eNB in the format defined in LTE/LTE-A standard. In LTE/LTE-A, theUE feedback information includes the following three indicators:

1. RI: number of spatial layers that can be supported by the currentchannel experienced at the UE

2. PMI: precoding matrix recommended by the current channel experiencedat the UE

3. CQI: maximum possible data rate that the UE can receive signals inthe current channel state. CQI may be replaced with the SINR, a maximumerror correction code rate and modulation scheme, or per-frequency dataefficiency that can be used in a similar way to the maximum data rate.

The RI, PMI, and CQI have associated meanings. For example, theprecoding matrix supported in LTE/LTE-A is configured differently perrank. Accordingly, the PMI value ‘X’ is interpreted differently for thecases of RI set to 1 and RI set to 2. Also, when determining CQI, the UEassumes that the PMI and RI, which it has reported, are applied by theeNB. Specifically, if the UE reports RI_X, PMI_Y, and CQI_Z; this meansthat the UE is capable of receiving the signal at the data ratecorresponding to CQI_Z when the rank RI_X and the precoding matrix PMI_Yare applied. In this way, the UE calculates CQI with which the optimalperformance is achieved in real transmission under the assumption of thetransmission mode to be selected by the eNB.

Typically, in FD-MIMO using a plurality of transmit antennas, the numberof CSI-RSs has to increase in proportion to the number of transmitantennas. For an LTE/LTE-A using 8 transmit antennas, the eNB has totransmit CSI-RSs of 8 ports to the UE for downlink channel statemeasurement. In order to transmit 8-port CSI-RSs, 8 REs must beallocated for CSI-RS transmission in one RB. For example, the REsindicated by A and B can be used for CSI-RS transmission of thecorresponding eNB. When applying a CSI-RS transmission scheme ofLTE/LTE-A to FD-MIMO, the CSI-RS transmission resource increases inproportion to the number of transmit antennas. Specifically, the eNBhaving 128 transmit antennas has to transmit CSI-RS on 128 REs in oneRB. Such a CSI-RS transmission scheme consumes excessive radioresources, and thus, causes a shortage of resources for datatransmission.

For the eNB having a plurality of transmit antennas, an FD-MIMO maytransmit CSI-RSs on N dimensions such that the UE performs channelmeasurements for a plurality of transmit antennas without excessiveresource allocation for CSI-RS transmission. As shown in FIG. 1 wherethe transmit antennas 110 of the eNB are arranged 2-dimensionally, theCSI-RSs may be transmitted as separated into 2 dimensions. One CSI-RS isused as a horizontal CSI-RS for acquiring the horizontal directionchannel information, while the other CSI-RS is used as a vertical CSI-RSfor acquiring vertical direction channel information.

FIG. 3 is a diagram illustrating a mechanism of CSI-RS transmission inFD-MIMO system, according to an embodiment of the present invention.

Referring to FIG. 3, the eNB operating in FD-MIMO mode has total 32antennas. The number of antennas may vary depending on the embodiment.In FIG. 3, 32 antennas 300 are indicated by A0, . . . , A3, B0, . . . ,B3, C0, . . . , C3, D0, . . . , D3, E0, . . . , E3, F0, . . . , F3, G0,. . . , G3, and H0, . . . , H3. Two CSI-RSs are transmitted through the32 antennas. The antenna ports corresponding to H-CSI-RS for use inmeasuring horizontal channel state consist of the following 8 antennaports.

1. H-CSI-RS port 0: group of antennas A0, A1, A2, and A3

2. H-CSI-RS port 1: group of antennas B0, B1, B2, and B3

3. H-CSI-RS port 2: group of antennas C0, C1, C2, and C3

4. H-CSI-RS port 3: group of antennas D0, D1, D2, and D3

5. H-CSI-RS port 4: group of antennas E0, E1, E2, and E3

6. H-CSI-RS port 5: group of antennas F0, F1, F2, and F3

7. H-CSI-RS port 6: group of antennas G0, G1, G2, and G3

8. H-CSI-RS port 7: group of antennas H0, H1, H2, and H3

The grouping a plurality of antennas into one CSI-RS port is a conceptreferred to as antenna virtualization. Typically, antenna virtualizationis performed through linear combination of a plurality of antennas. Theantenna ports corresponding to V-CSI-RS for use in measuring verticalchannel state consist of the following 4 antenna ports.

1. V-CSI-RS port 0: group of antennas A0, B0, C0, D0, E0, F0, G0, and H0

2. V-CSI-RS port 1: group of antennas A1, B1, C1, D1, E1, F1, G1, and H1

3. V-CSI-RS port 2: group of antennas A2, B2, C2, D2, E2, F2, G2, and H2

4. V-CSI-RS port 3: group of antennas A3, B3, C3, D3, E3, F3, G3, and H3

It is assumed that a plurality of antennas are arranged 2-dimensionallyas described above. The antennas are arranged orthogonally forming Mrows in the vertical direction and N columns in the horizontaldirection. The UE is capable of measuring FD-MIMO channels using NH-CSI-RS ports and M V-CSI-RS ports. As aforementioned, if two CSI-RSsare used, the channel state information can be acquired using M+N CSI-RSports for M×N transmit antennas. Since the channel information on alarge number of transmit antennas is acquired using a relatively smallnumber of CSI-RS ports, it is advantageous in reducing the CSI-RSoverhead. Although embodiments of the present invention are directed tochannel information on the FD-MIMO transmit antennas using two CSI-RSs,this approach can be applied to the cases of using two or more CSI-RSs.

In FIG. 3, the RSs of the 32 transmit antennas are mapped to 8 H-CSI-RSports and 4 V-CSI-RS ports, and the UE measures the radio channels usingthe CSI-RSs of the FD-MIMO system. The H-CSI-RS can be used forestimating the horizontal angle between the UE and the eNB transmitantennas as denoted by reference numeral 310, while the V-CSI-RS can beused for estimating the vertical angle between the UE and the eNBtransmit antennas as denoted by reference numeral 320.

The following abbreviations are used throughout the specification.

-   -   RI_(H): RI generated based on H-CSI-RS for feedback to the eNB    -   RI_(V): RI generated based on V-CSI-RS for feedback to the eNB    -   RI_(HV): RI generated based on H-CSI-RS and V-CSI-RS for        feedback to the eNB    -   PMI_(H): PMI generated based on H-CSI-RS for feedback to the eNB    -   PMI_(V): PMI generated based on V-CSI-RS for feedback to the eNB    -   CQI_(H): UE-recommended data rate generated under the assumption        that only the horizontal direction precoding matrix is applied    -   CQI_(V): UE-recommended data rate generated under the assumption        that only the vertical precoding matrix is applied    -   CQI_(HV): UE-recommended data rage generated under the        assumption that both the horizontal and vertical precoding        matrices are applied

The following description is directed to the case of using thehorizontal direction channel state information and the verticaldirection channel state information. When an eNB operates with two ormore CSI-RSs, however, other types of channel state information can alsobe applied to the horizontal and vertical direction channel stateinformation. In an embodiment of the present invention where the CSI-RSmapped to an antenna port from the first view point (first CSI-RS) andthe CSI-RS mapped to an antenna port from the second view point (secondCSI-RS) are used, the UE is capable of acquiring the channel stateinformation (first and second channel state information) based on thetwo respective CSI-RSs and the channel state information (third channelstate information) based on both the CSI-RSs. The configurationdescribed in the following description is applicable to variousembodiments in similar manner. The following description is directed toan embodiment of the present invention using V-CSI-RS and H-CSI-RS.

In the following description, the channel state informationcorresponding to the vertical direction CSI-RS is referred to asvertical direction channel state information. The vertical directionchannel state information includes at least one of RI, PMI, and CQIacquired based on the vertical direction CSI-RS.

In the following description, the channel state informationcorresponding to the horizontal direction CSI-RS is referred to ashorizontal direction channel state information. The horizontal channelstate information includes at least one of RI, PMI, and CQI acquiredbased on the horizontal direction CSI-RS.

When the eNB sends the UE two or more CSI-RSs, the UE is capable oftransmitting the channel state information corresponding to therespective CSI-RSs. Each of the channel state information includes atleast one of RI, PMI, and CQI. However, the UE may acquire the channelstate information based on the two or more CSI-RSs in an embodiment ofthe present invention. Acquisition of the channel state information isdescribed in greater detail below.

FIG. 4 is a diagram illustrating a mechanism of transmitting RI, PMI,and CQI based on two CSI-RS in the feedback method, according to anembodiment of the present disclosure. The UE reports the radio channelstate information of the FD-MIMO to the eNB by transmitting RI, PMI, andCQI for the respective CSI-RSs.

In FIG. 4, the arrow indicates how a certain type of channel stateinformation is related to other types of channel state information. Thearrow starting from RIv 400 and ending at PMIv 410 indicates that thePMIv 410 is interpreted differently according to the value of RIv 400.Specifically, the arrow means that the UE uses the value of the RI_(V)400 to interpret CQI_(V) 420. Likewise, the UE uses the value of RI_(H)430 to interpret PMI_(H) 440.

In FIG. 4, the UE measures the V-CSI-RS and transmits the channel stateinformation in the method indicated by “Feedback 1”. The UE alsomeasures the H-CSI-RS and transmits the channel state information in themethod indicated by “Feedback 2”. Here, RI, PMI, and CQI are transmittedin the state of being correlated among each other. In the case of“Feedback 1”, the RI_(V) 400 notifies of the rank of the precodingmatrix indicated by the PMI_(V) 410. Also, the CQI_(V) 420 indicates thedata rate at which the UE can receive data or a corresponding value inthe case of applying the precoding matrix of the corresponding rankwhich is indicated by the PMI_(V) 410, when the transmission isperformed at the rank indicated by the RI_(V) 400. In the case of“Feedback 2”, the RI 430, the PMI 440, and CQI 450 are transmitted inthe state of being correlated among each other like the case of“Feedback 1”.

As shown in FIG. 4, one of the channel state information report methodsmay configure a plurality of feedback for a plurality of transmitantennas of the FD-MIMO eNB, and make the UE report channel stateinformation to the eNB. This method is advantageous in that the UE iscapable of generating and reporting channel state information forFD-MIMO without extra implementation.

However, in the channel state information report method of FIG. 4, it isdifficult to achieve enough throughput of the FD-MIMO system. This isdue to the fact that although the UE configures a plurality of feedbackto report the channel state information to the eNB, the CQI is generatedwithout an assumption on the precoding when the FD-MIMO is applied.

When a plurality of transmit antennas 110 of the FD-MIMO system arearranged 2-dimentionally, as shown in FIG. 3, both the verticaldirection precoding matrix and the horizontal direction precoding matrixare applied to the signal transmitted by the UE. Specifically, the UEreceives the signal to which the precoding matrices corresponding to thePMI_(H) 440 and the PMI_(V) 410 other than the signal to which one ofthe PMI_(H) 440 and the PMI_(V) 410.

If only the CQI_(H) 450 and the CQI_(V) 420 corresponding to precodingsindicated by the respective PMI_(H) 440 and PMI_(V) 410 are reported tothe eNB, the eNB has to determine the CQI to which both the vertical andhorizontal direction precoding matrices are applied, without receipt ofsuch a CQI. If the eNB determines the CQI to which both the vertical andhorizontal direction precoding matrices are applied arbitrarily, thismay cause degradation of system performance.

As described above, one of the methods for mitigating the use of radioresource for CSI-RS transmission in the FD-MIMO system is to make the UEmeasure a plurality CSI-RSs capable of efficiently estimating aplurality of transmit antennas. Each CSI-RS can be used for the UE tomeasure the channel state of one of a plurality dimensions for measuringone radio channel. This method requires a relatively small amount ofradio resources for CSI-RS transmission as compared to the method ofallocating a unique CSI-RS ports for the respective transmit antennas.For example, when using two CSI-RSs in the vertical and horizontaldirection for the transmit antennas of the FD-MIMO that are arranged inthe form of a rectangle, the UE is capable of efficiently measuring thechannel state. Embodiments of the present invention propose a noveltechnology and apparatus that is capable of allowing the UE to measure aplurality of CSI-RSs and efficiently report the channel stateinformation in the FD-MIMO system including a plurality of transmitantennas.

FIG. 5 is a diagram illustrating a mechanism of transmitting channelstate information, according to an embodiment of the present disclosure.

In FIG. 5, the channel state information corresponding to the twoCSI-RSs are reported as in the embodiment of FIG. 4. The channel stateinformation transmission method is indicated by “Feedback 1” as in theembodiment of FIG. 4. Specifically, the UE measures V-CSI-RS to reportRI_(V) 500, PMI_(V) 510, and CQI_(V) 520 to the eNB. The embodiment ofFIG. 5 differs from the embodiment of FIG. 4 in the procedure ofindication with “Feedback 2”. The UE reports the CQI for the case wherethe precoding is applied in both the vertical and horizontal directions,i.e., CQI_(HV) 550, to the eNB. Specifically, the UE reports to the eNBthe most recent PMI_(V) 510 generated in the procedure indicated with“Feedback 1” and CQI_(HV) 550 generated in the case where the precodingsindicated by PMI 540, which is determined optimal based on the H-CSI-RSmeasurement.

In the embodiment of FIG. 5, the UE measures the V-CSI-RS to generatethe RI_(V) 500, which is reported to the eNB. The UE determines thePMI_(V) 510 optimal to the corresponding rank 500 and reports theCQI_(V) 520 when the precoding indicated by the PMI_(V) 510 is applied.The UE measures H-CSI-RS to generate RI 530, which is reported to theeNB. The UE reports to the eNB the CQI_(HV) 550 generated by applyingthe precoding indicated by PMI 540 optimal to the corresponding rank 530and the precoding indicated by the previously transmitted PMI_(V) 510.

As shown in FIG. 5, in order for the UE to report the CQI value for thecase where the precoding matrix indicated by the PMI_(H) 540 and theprecoding matrix indicated by the PMI_(V) 510 are allocatedsimultaneously to the eNB, the following may be required.

First, it is required to define a function for determining whether totake two PMIs into consideration to determine at least one of two CQIs.Specifically, the eNB notifies the UE of the correlation of the feedbackinformation in configuring a plurality of feedbacks to the UE, and theUE generates CQI based thereon. In the case of FIG. 5, a control messageinstructing to calculate the second CQI, i.e., the CQI_(HV) 550, byapplying the first PMI, i.e. the PMI_(V) 510, and the second PMI, i.e.the PMI_(H) 540, together has to be transmitted from the eNB to the UE.

Second, it is required to define how to determine CQI in the case ofapplying a plurality of precodings. When calculating a CQI when only oneprecoding is applied, the UE calculates CQI under the assumption thatthe precoding indicated by RI and PMI it has reported is applied indownlink. However, in the case of the CQI_(HV) 550, the UE calculatesCQI under the assumption that two precodings are simultaneously appliedin downlink. The UE may interpret the application of two precodings asthe Kronecker product. The Kronecker product is defined with twomatrices as shown in Equation (1) below.

$\begin{matrix}{{A \otimes B} = \begin{bmatrix}{a_{11}B} & \ldots & {a_{1n}B} \\\vdots & \ddots & \vdots \\{a_{m\; 1}B} & \ldots & {a_{mn}B}\end{bmatrix}} & (1)\end{matrix}$

In Equation (1), A and B denote matrices, and a₁₁ to a_(mn) denoteelements of matrix A, and a_(ij) denotes the element at i_(th) row andj_(th) column.

In Equation (1), the UE is capable of acquiring the precoding matrix forthe case where two precoding matrices are applied simultaneously byreplacing A and B with the precoding matrices indicated by the PMI_(H)540 and the PMI_(V) 510. When calculating the CQI_(HV) 550, the UEcalculates the CQI_(HV) 550 under the assumption that the precodingmatrix acquired by applying the Equation (1) to the precoding matricesindicated by the PMI_(H) 540 and PMI_(V) 510 is applied in downlink.

In order to acquire the precoding matrix for the case where the twoprecoding matrices are applied using the Kronecker product of Equation(1), it is necessary for the UE and eNB to operate differently dependingon the rank reported by the UE. Three embodiments are proposed for thispurpose.

Rank-Related Embodiment 1

The eNB configures one of the RI_(V) 500 and the RI_(H) 530 with rank 1always. For example, if the CQI_(HV) 550 is reported along with theRI_(H) 530 to the eNB, the RI_(V) 500 is restricted to be always setto 1. The rank supported in the case where two precoding matrices areapplied simultaneously is determined depending on the RI_(H) 530.Specifically, when the RI_(H) 530 is set to 1, the UE is capable ofsupporting rank 1; and when the RI_(H) 530 is set to 2, the UE iscapable of supporting rank 2. The UE and the eNB operate in the FD-MIMOsystem under this assumption. Although two CSI-RSs are assumed in thisembodiment of the present invention, if the number of CSI-RS is 3 ormore, RIs have to be set to 1 with the exception of the RI correspondingto one CSI-RS.

Rank-Related Embodiment 2

When the vertical and horizontal direction precoding matrices areapplied simultaneously, the eNB and the UE determine the ranksupportable by the UE using Equation (2) set forth below.

rank_(HV)=rank(RI _(H))×rank(RI _(V))   (2)

Specifically, the UE and the eNB exchange the channel state informationunder the assumption that the rank for the case where the vertical andhorizontal direction precoding matrices are applied simultaneously isthe product of the two ranks supportable in the respective directions.For example, if the UE reports the RI_(H) set to 2 and RI_(V) set to 3to the eNB, the eNB and the UE assume that the rank for the case whereall of the precoding matrices are applied is 6.

In LTE/LTE-A, if the UE reports to the eNB the RI corresponding to rank2 or higher, two CQI values are reported to the eNB. This is due to thefact that the eNB transmits two codewords to the UE, and thus, the UEhas to separately report the CQIs corresponding to respective codewords.

When the method of Equation (2) is applied to the embodiment of FIG. 5,if the rank for the case where the precodings obtained by Equation (2)is 2 or higher although the RI_(H) 530 is set to 1, the UE transmits thetwo CQIs in the form of the CQI_(HV) 550. Also, if the rank for the casewhere all of the precodings obtained by Equation (2) is 2 or higher, theeNB receives the two CQIs under the assumption that they are transmittedin the form of the CQI_(HV) 550.

In the method of measuring, at the UE, the horizontal and verticaldirection channel state information corresponding to two CSI-RS andreporting the channel state information to the eNB, as shown in FIG. 4or 5, transmission of “Feedback 1” and “Feedback 2” may cause collision.The term ‘collision’ refers to a situation in which transmission of“Feedback 1” and “Feedback 2” is required at the same time. If anycollision is predicted, the UE may report the channel state informationof one of “Feedback 1” and “Feedback 2”. The FD-MIMO operation with theconfiguration of a plurality of feedback, as shown in FIG. 4 or 5, maycause the channel state information to be partially missed.

FIG. 6 is a diagram illustrating a mechanism of transmitting channelstate information, according to an embodiment of the present invention.

Although the UE reports the channel state information corresponding totwo CSI-RSs, the feedback method of FIG. 6 differs from that of FIG. 4in that the feedback is completed in only one feedback process.Referring to FIG. 6, the UE transmits RI_(HV) 600 to report thehorizontal and vertical direction ranks Table 1 shows horizontal andvertical direction ranks (first second ranks)

TABLE 1 RI_(HV) Horizontal direction rank Vertical direction rank 000 11 001 2 1 010 3 1 011 4 1 100 1 2 101 2 2 110 3 2 111 4 2

The eNB may acquire the horizontal and vertical direction ranks from theRI_(HV) 600 transmitted by the UE. The UE determines the value of theRI_(HV) 600 based on both the two CSI-RS, i.e., H-CSI-RS and V-CSI-RS.The eNB checks the information on the horizontal and vertical directionprecodings and UE-supportable data rate based on PMIs 610 and 630 andCQIs 620 and 640 corresponding to the H-CSI-RS and V-CSI-RS. Since thehorizontal and vertical direction PMIs and CQIs are transmittedalternately in one feedback process, it is possible to avoid thecollisions of the feedback transmissions that may occur in theembodiments of FIGS. 4 and 5. In FIG. 6, the horizontal and verticaldirection ranks may have different values depending on the value of theRI_(HV) 600 reported by the UE. Specifically, the precoding matrixindicated by the PMI_(H) 610 is determined depending on the horizontaldirection PMI indicated by the value of the RI_(HV) 600. The UE alsotransmits CQI obtained under the assumption of the case where theprecoding matrix indicated by the RI_(H) 610 is applied, i.e., theCQI_(H) 620. In order to determine the values of the PMI_(H) 610 and theCQI_(H) 620, the UE measures the H-CSI-RS. Likewise, the precodingmatrix indicated by the PMI_(V) 630 is determined depending on thevertical direction rank indicated by the RI_(HV) 600. The UE alsotransmits CQI obtained under the assumption of the case where theprecoding matrix indicated by the PMI_(V) 630 is applied, i.e., theCQI_(V) 640. In order to determine the values of PMI_(V) 630 and CQI_(V)640, the UE measures V-CSI-RS.

Referring to FIG. 6, the UE alternately transmits the horizontal channelstate information 610 and 620 and the vertical channel state information630 and 640. It is also possible to alternately transmit the horizontaland vertical channel state information in the same interval.

In a real system, however, such a method may not be appropriate.Specifically, it may advantageous for the UE to report specificdirection channel state information at an interval shorter than that ofthe other direction channel state information in view of systemthroughput optimization. In order for the UE to report channel stateinformation corresponding to a plurality of CSI-RSs to the eNB atdifferent intervals, it is preferred for the eNB to performconfiguration thereon. Specifically, in the case that the UE reportsdifferent direction channel state information to the eNB in one feedbackprocess, the eNB may notify the UE of the following information forconfiguration thereon.

-   -   Feedback interval and frame offset for horizontal direction        channel state information (CQI_(H), PMI_(H)), i.e., first        channel state information    -   Feedback interval and frame offset for vertical direction        channel state information (CQI_(V) and PMI_(V)), i.e., second        channel state information

The subframe offset value is the value determining the subframe positionfor real transmission in a period. For example, if the period is 10milliseconds (msec) and the subframe offset is 5, this means that thecorresponding signal is transmitted at the subframe 5 in the period of10 milliseconds.

In FIG. 6, the horizontal and vertical direction ranks reported from theUE to the eNB may be determined depending on different rankrestrictions. The rank restriction is to restrict, when the UE measuresthe RS to determine the rank, the maximum value to the valuepreconfigured by the eNB. In the mobile communication system, if the eNBis allowed to restrict the maximum value of the rank for the UE, it canbe interpreted as a part of the optimization procedure for controllingthe system in the eNB-preferred way. In order to apply the rankrestriction to the respective horizontal and vertical direction ranks,the eNB may notify the UE of the following information through higherlayer signaling or in another method.

1. Maximum value of horizontal direction rank

2. Maximum value of vertical direction rank

FIG. 7 is a diagram illustrating a mechanism of transmitting channelstate information, according to another embodiment of the presentinvention. In the embodiment of FIG. 7, the UE reports the channel stateinformation to the eNB in one feedback process as in the embodiment ofFIG. 6. However, the embodiment of FIG. 7 differs from the embodiment ofFIG. 6 in that the horizontal and vertical direction ranks are reportedwith RI_(H) 700 and RI_(V) 730 separately, rather than with RI_(HV) 600.

Referring to FIG. 7, the RI_(H) 700 is reported and then followed byPMI_(H) 710 and CQI_(H) 720 based thereon. Also, the RI_(V) 730 isreported and then followed by PMI_(V) 740 and CQI_(V) 750 based thereon.Although the RI_(H) 700 and the RI_(V) 730 are reported separately, theintervals and ranks of the horizontal and vertical channel stateinformation may be configured differently, as in the embodiment of FIG.6.

FIG. 8 is a diagram illustrating a mechanism of transmitting channelstate information, according to another embodiment of the presentinvention.

When the UE reports the channel state information corresponding to aplurality of CSI-RSs in a signal feedback process, as in the embodimentsof FIGS. 6 and 7, the absence of the CQI for the case where thehorizontal and vertical direction precodings are applied simultaneouslymay cause system performance degradation, as described above.

Referring to FIG. 8, the UE transmits RI_(HV) 800 to the eNB. The eNBmay acquire or recognize the horizontal and vertical direction ranksbased on the RI_(HV) 800. The UE transmits the horizontal directionchannel state information including PMI_(H) 810 and CQI_(H) 820. The UEalso transmits PMI_(V) 830 as the horizontal channel state information,and then the CQI is acquired by taking both the horizontal and verticaldirection precodings into account, i.e., CQI_(HV) 840, along with thePMI_(V) 830 simultaneously. The CQI_(HV) 840 is the CQI acquired for thecase where the horizontal and vertical direction precodings are applied.Accordingly, the rank is also determined as the function of thehorizontal and vertical direction ranks The UE assumes the Kroneckerproduct of the two precoding matrices as shown in Equation (1) as theprecoding applied for generating the CQI_(HV) 840.

This method of transmitting the horizontal and vertical directionchannel state information and the CQI_(HV) 840 from the UE to the eNB ina signal feedback process, as shown in FIG. 8, makes it possible totransmit the value of the CQI_(HV) 840 under the assumption of theapplication of horizontal and vertical direction precodings. However,this method has a shortcoming in that the CQI_(H) 820 generated underthe assumption of the application of only the horizontal directionprecoding has a low degree of utilization. In FIG. 8, the reason fortransmitting the CQI_(H) 820 is because the information on the PMI_(H)810 and the PMI_(V) 830 is required for transmitting CQI assuminghorizontal and vertical direction precodings, but only one of the PMIscan be reported at the time of transmitting the CQI_(H) 820.

FIG. 9 is a diagram illustrating a mechanism of transmitting channelstate information, according to another embodiment of the presentinvention.

In the channel state information transmission method of FIG. 9, all CQIvalues reported from the UE to the eNB are generated under theassumption that the horizontal and vertical direction precodings areapplied unlike the embodiment of FIG. 8. In FIG. 9, the UE generatesCQI_(HV) 930 under the assumption that the horizontal and verticalprecoding matrices have been applied as indicated by PMI_(V) 900 andPMI_(H) 920. Specifically, the UE generates the CQI_(HV) 930 transmittedalong with the PMI_(H) 920 under the assumption that both the precodingmatrix indicated by the PMI_(V) 900, as the most recently transmittedvertical direction precoding-related information, and the precodingmatrix indicated by the PMI_(H) 920 have been applied. Likewise, the UEgenerates CQI_(HV) 950 transmitted along with PMI_(V) 940 under theassumption that both the precoding matrix indicated by the PMI_(H) 920,as the most recently transmitted horizontal direction precoding-relatedinformation, and the precoding matrix indicated by the PMI_(V) 940 havebeen applied. The reason for referencing the previously transmittedPMI_(H) or PMI_(V) is to prevent a plurality of PMIs from beingtransmitted in one time duration.

In order to transmit CQI_(HV) at every CQI transmission occasion, asshown in FIG. 9, it is necessary to restrict the rank in a specificdirection. In order to change the horizontal and vertical directionranks simultaneously, the horizontal and vertical direction precodingsalso have to be updated according to the changed rank values. CQI_(HV)may be transmitted only after the two precodings have been updated. Bytaking notice of this, it is assumed that the vertical direction rank isfixed to 1 always in the embodiment of FIG. 9. Since the verticaldirection rank is always 1, the vertical direction rank is not changed,such that the UE is capable of assuming that the precoding matrixindicated by the previously transmitted PMI_(V) and the precoding matrixindicated by PMI_(V) are applied simultaneously. Although thedescription is directed to the case where the vertical direction rank isfixed to 1, the present invention may be embodied in such a way to fixthe horizontal direction rank to 1. When the horizontal direction rankis fixed to 1, the UE reports RI_(V) at every RI transmission occasioninstead of RI_(H).

In FIG. 9, the transmission intervals of RI, horizontal directionchannel state information 920 and 930, vertical direction channel stateinformation 940 and 950, may be configured differently depending on thesystem environment.

FIG. 10 is a diagram illustrating a mechanism of transmitting channelstate information, according to another embodiment of the presentinvention.

In FIG. 10, the UE transmits CQI_(HV) under the assumption that thehorizontal and vertical direction precodings are applied at every CQItransmission occasion as in FIG. 9. In the embodiment of FIG. 10,however, an extra RI_(V) 1000 is transmitted to change the verticaldirection rank. Specifically, the UE notifies the eNB of the verticaldirection rank to the eNB using the RI_(V) 1000 and reports PMI_(V) 1010based thereon. CQI_(HV) 1020 transmitted along with the PMI_(V) 1010 isgenerated under the assumption that the precoding matrix indicated bythe most recently transmitted RI and PMI and the precoding matrixindicated by the PMI_(V) 1010 are applied. When the horizontal directionrank is updated with RI_(H) 1030, the UE updates PMI_(H) 1040 basedthereon and generates CQI_(HV) 1050 under the assumption that theprecoding indicated by the PMI_(V) 1010 and the precoding indicated bythe PMI_(H) 1040 are applied simultaneously.

In FIG. 10, the UE may separately update the horizontal and verticaldirection ranks Accordingly, the UE calculates the rank to be assumedfor generating the channel state information CQI_(HV) 1020 and 1050using Equation (2). If the product of the ranks indicated by the RI_(V)1000 and the RI_(H) 1030 is assumed as the rank for generating theCQI_(HV) 1050. Accordingly, if the product of the ranks indicated by theRI_(V) 1000 and the RI_(H) 1030 at the time when the CQI_(HV) 1050 istransmitted is 1, the UE transmits one CQI. If the product is equal toor greater than 2, the UE transmits two CQIs.

FIG. 11 is a flowchart illustrating an eNB procedure of configuringchannel state information feedback of the UE in a FD-MIMO system,according to an embodiment of the present invention.

In FIG. 11, the eNB checks the number of transmit antennas of theFD-MIMO transmitter and 2-dimensional arrangement state, in step 1100.The eNB determines how to configure the horizontal and vertical CSI-RSsfor use in measuring the FD-MIMO channel state information, in step1110. Although CSI-RS_(H) and CSI-RS_(V) are configured in an embodimentof the present invention, the present invention may be embodied in sucha way of configuring a first type CSI-RS and a second CSI-RS in anotherformat. The configuration on CSI-RS_(H) and CSI-RS_(V) are informed tothe UE through higher layer signaling or in another method, in step1120. The eNB notifies the UE of the feedback scheme for the UE totransmit the channel state information corresponding to the CSI-RS_(H)and CSI-RS_(V), in step 1130. Finally, the eNB receives the CSI-RS_(H)and CSI-RS_(V) transmitted by the UE, in step 1140. The eNB controls thesystem operation including scheduling based on the received channelstate information.

FIG. 12 is a flowchart illustrating a UE procedure for transmitting thechannel state information based on the configuration indicated by theeNB in the FD-MIMO system, according to an embodiment of the presentdisclosure.

The UE receives the information on how to receive the horizontal andvertical direction CSI-RSs, i.e., CSI-RS_(H) and CSI-RS_(V), from theeNB, in step 1200. Although CSI-RS_(H) and CSI-RS_(V) are configured inan embodiment of the present invention, the present invention may beembodied in such a way of configuring a first type CSI-RS and a secondCSI-RS in another format. The UE receives CSI feedback configurationinformation on how to measure the CSI-RS_(H) and CSI-RS_(V) and reportsthe channel state information, in step operation 1210. The UE measuresthe CSI-RSH and CSI-RSV and transmits channel state informationaccording to the CSI feedback configuration information, in step 1220.The channel state information is generated and transmitted as describedwith reference to FIGS. 5 to 10.

Although the embodiments of FIGS. 11 and 12 are directed to anembodiment in which the eNB transmits CSI-RS and channel stateinformation feedback configuration explicitly, the present invention maybe embodied in such a way that the eNB notifies the UE of at least oneof CSI-RS transmission position of the eNB, number of CSI-RSs, andnumber of ports per CSI-RS, and the UE generates and transmits thechannel state information according to a feedback configurationpredetermined based on the received information. It is enough for theeNB to provide the UE with the information necessary for determining thechannel state information generation and transmission method.

FIG. 13 is a block diagram illustrating a configuration of the eNB,according to an embodiment of the present invention.

As shown in FIG. 13, the eNB includes a controller 1300, a transmitter1310, and a receiver 1320. The controller 1300 determines theconfiguration on the plurality of CSI-RSs. The controller 1300 maydetermine the CSI-RS transmission scheme and the corresponding channelstate information generation and feedback scheme. The transmitter 1310transmits the determination result to the UE. The transmitter 1310transmits the plurality of CSI-RSs to the UE. The receiver 1320 receivesthe channel state information corresponding to the CSI-RSs from the UE.

FIG. 14 is a block diagram illustrating a configuration of the UE,according to an embodiment of the present invention.

A receiver 1420 receives the configuration information on the pluralityof CSI-RSs, and channel state information generation and feedbackscheme. A controller 1400 controls the receiver 1420 to receive theplurality of CSI-RSs transmitted by the eNB. The controller 1400generates channel state information based on the plurality of CSI-RSs.The controller 1400 controls a transmitter 1410 to transmit the channelstate information to the eNB.

As described above, the channel state information feedback method of thepresent invention is capable of transmitting/receiving channel stateinformation efficiently in a wireless system using a plurality ofantennas.

It will be understood that each block of the flowchart illustrationsand/or block diagrams, and combinations of blocks in the flowchartillustrations and/or block diagrams, can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a general purpose computer, special purposecomputer, or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the flowchartand/or block diagram block or blocks. These computer programinstructions may also be stored in a computer-readable memory that candirect a computer or other programmable data processing apparatus tofunction in a particular manner, such that the instructions stored inthe computer-readable memory produce an article of manufacture includinginstruction means which implement the function/act specified in theflowchart and/or block diagram block or blocks. The computer programinstructions may also be loaded onto a computer or other programmabledata processing apparatus to cause a series of operational steps to beperformed on the computer or other programmable apparatus to produce acomputer implemented process such that the instructions which execute onthe computer or other programmable apparatus provide steps forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

Furthermore, the respective block diagrams may illustrate parts ofmodules, segments or codes including at least one or more executableinstructions for performing specific logic function(s). Moreover, itshould be noted that the functions of the blocks may be performed indifferent order in several modifications. For example, two successiveblocks may be performed substantially at the same time, or may beperformed in reverse order according to their functions.

The term “module” according to embodiments of the present invention,means, but is not limited to, a software or hardware component, such asa Field Programmable Gate Array (FPGA) or Application SpecificIntegrated Circuit (ASIC), which performs certain tasks. A module mayadvantageously be configured to reside on the addressable storage mediumand configured to be executed on one or more processors. Thus, a modulemay include, by way of example, components, such as software components,object-oriented software components, class components and taskcomponents, processes, functions, attributes, procedures, subroutines,segments of program code, drivers, firmware, microcode, circuitry, data,databases, data structures, tables, arrays, and variables. Thefunctionality provided for in the components and modules may be combinedinto fewer components and modules or further separated into additionalcomponents and modules. In addition, the components and modules may beimplemented such that they execute one or more CPUs in a device or asecure multimedia card.

While the invention has been shown and described with reference tocertain embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail may be made thereinwithout departing form the spirit and scope of the invention as definedby the appended claims.

What is claimed is:
 1. A method for transmitting channel stateinformation of a terminal, the method comprising the steps of: receivinga first Channel State Information Reference Signal (CSI-RS) and a secondCSI-RS; generating Channel State Information (CSI) based on both thefirst CSI-RS and the second CSI-RSs; and transmitting the CSI.
 2. Themethod of claim 1, wherein generating the CSI comprises: acquiring afirst Precoding Matrix Indicator (PMI) corresponding to the first CSI-RSand a second PMI corresponding to the second CSI-RS; and acquiring aChannel Quality Indicator (CQI) when the first PMI and the second PMIare applied as the CSI.
 3. The method of claim 1, wherein generating theCSI-RS comprises: acquiring a first Rank Indicator (RI) corresponding tothe first CSI-RS and a second RI corresponding to the second CSI-RS; andgenerating a third RI by combining the first RI and the second RI as theCSI.
 4. The method of claim 1, wherein the first CSI-RS corresponds toantenna ports aligned linearly in a first direction among antennasarranged in a grid formation, and the second CSI-RS corresponds toantenna ports aligned linearly in a second direction among the antennasarranged in the grid formation.
 5. The method of claim 2, furthercomprising: transmitting the first PMI at a first time; and transmittingthe second PMI at a second time, wherein transmitting the CSI comprisestransmitting the CQI and the second PMI at a same time.
 6. The method ofclaim 1, wherein generating the CSI comprises: receiving an indicatorthat indicates whether to consider both the first CSI-RS and the secondCSI-RS in generating the CSI; and when the indicator indicates toconsider both the first CSI-RS and the second CSI-RS, generating the CSIby taking both the first CSI-RS and the second CSI-RS intoconsideration.
 7. A terminal for transmitting channel state information,the terminal comprising: a receiver that receives a first Channel StateInformation Reference Signal (CSI-RS) and a second CSI-RS; a controllerthat generates Channel State Information (CSI) based on both the firstCSI-RS and the second CSI-RS; and a transmitter that transmits the CSI.8. The terminal of claim 7, wherein the controller acquires a firstPrecoding Matrix Indicator (PMI) corresponding to the first CSI-RS and asecond PMI corresponding to the second CSI-RS, and acquires a ChannelQuality Indicator (CQI) when the first PMI and the second PMI areapplied as the CSI.
 9. The terminal of claim 8, wherein the controlleracquires a first Rank Indicator (RI) corresponding to the first CSI-RSand a second RI corresponding to the second CSI-RS and generates a thirdRI by combining the first RI and the second RI as the CSI.
 10. Theterminal of claim 8, wherein the first CSI-RS corresponds to antennaports aligned linearly in a first direction among antennas arranged in agrid formation, and the second CSI-RS corresponds to antenna portsaligned linearly in a second direction among the antennas arranged inthe grid formation.
 11. The terminal of claim 9, wherein the transmittertransmits the first PMI at a first time, and transmits the second PMIand the CQI simultaneously at a second time.
 12. The terminal of claim1, wherein the receiver receives an indicator that indicates whether toconsider both the first CSI-RS and the second CSI-RS in generating theCSI and, when the indicator indicates to consider both the first CSI-RSand the second CSI-RS, generates the CSI by taking both the first CSI-RSand the second CSI-RS into consideration